Chlorobiphenylyl ether



May 14, 1963 R. G. SCHULTZ ETAL 3,089,987

DIELECTRIC COMPOSITIONS AND PROCESS Filed May 4, 1961 Fig-E CONTA'NING ELECTRODES A MIXTURE 0F CHLORINATED BIPHENYL AND ISOPROPYL CHLOROBIPHENYLYL ETHER METAL FOIL PAPER IMPREGNATED WITH A MIXTURE OF CHLORINATED BIPHENYL AND METHYL Fig- 3 CHLOROBIPHENYLYL ETHER INVENTORS ROBERT e. SCHULTZ VAN R. GAERTNER ATTORNEY United States Patent 3,089,987 DIELECTRR CUMPGSlTlUNS AND PRGCEdEi Robert G. Schultz and Van R. Gael-titer, both of Dayton,

Ulric, assignors to Monsanto Chemical (Iompany, St- Louis, Mo., a corporation of Delaware Filed May 4, 1961, Ser. No. 107,775 14 Qlaims. (Q1. 317-450) This invention relates to chlorine-containing ethers and more particularly provides certain hitherto unknown alkyl chlorobiphenylyl ethers, the method of preparing the same, and dielectric compositions comprising said ethers.

Liquid chlorinated biphenyl compositions have been used for some time as electrical insulating materials be cause of their high dielectric constants, low electrical loss, thermal stability, resistance to oxidation, non-flammability, and other valuable properties. These chlorinated biphenyls are usually a mixture of chlorinated biphenyls wherein the degree of chlorination is most conveniently designated on an average basis, that is, the chlorinated biphenyl composition comprises a mixture of partially chlorinated biphenyl compounds having an average of, say, from about 2 to about 5 chlorine atoms in each biphenyl nucleus. They comprise mixtures not only of trichlorobiphenyls and tetrachlorobiphenyls but also of varying quantities of mono-, di-, penta-, hexa-, heptachlorobiphenyls, etc. Such chlorinated biphenyls are conveniently defined as having from say 35 percent to 55 percent by weight of combined chlorine and are available in commerce under the designation Aroclor, various types of Aroclor having more or less combined chlor1ne.

It is an object of this invention to provide liquid alkyl chlorinated biphenyl ether compositions having improved dielectric constants. It is another object of this invention to provide a process for preparing liquid alkyl chlorobiphenylyl ether compositions. Yet another object of this invention is to provide a process for improving the dielectric constant of liquid chlorinated biphenyl-containing materials. Another important object of this invention is to provide improved heat-transfer and dielectric compositions comprising an alkyl chlorobiphenylyl ether. Other objects and advantages of this invention will become apparent from a reading of the specification and claims hereinbelow.

In general it has been found according to this invention, that certain chlorinated biphenyl compounds, Aroclors of the above-defined types, can be chemically modified to produce new liquid compositions by treating them with an alkali metal alkoxide in a particular type of solvent to introduce one or more alkoxy groups into the biphenyl nucleus by replacing chlorine atoms therefrom to produce a mixture of the chlorinated biphenyl and alkyl chlorobiphenylyl ethers, which mixture has a significantly greater dielectric constant than the starting chlorinated biphenyl compositions.

More particularly, this invention provides new liquid alkyl chlorobiphenylyl ether compositions which are particularly useful for heat transfer and dielectric purposes. Those of the compositions which have a dielectric constant of about 6 or higher at 25 C. and at up to 100,000 cycles per second are a mixture of chlorinated biphenyls and alkyl chlorobiphenylyl ethers having from 1 to 4 carbon atoms in the alkyl radical, the compositions containing from about 15 percent to about 50 percent of combined chlorine and an average of about 0.1 to 2.0 alkoxy groups per biphenyl nucleus based on the total compositions. Compositions having an average of from about 0.5 to about 1.5 alkoxy groups per biphenyl nucleus and an average combined chlorine content of from about 20 percent to about 50 percent by weight are preferred,

with compositions having an average of about 0.6 to about 1.0 alkoxy groups per biphenyl nucleus and from about 25 percent to about 45 percent of combined chlorine being considered optimum for dielectric purposes. These compositions are prepared according to this invention by reacting a chlorinated biphenyl composition having from about 35 percent to about 55 percent of combined chlorine with an alkali metal alkoxide having from 1 to 4 carbon atoms in the alkoxide groups, employing as diluent a dialkyl ether of alkylene glycol having from 1 to 4 alkylene groups and from 2 to 4 carbon atoms in each alkylene group.

The al'kyl chlorobiphenylyl ether component of the compositions of this invention is a mixture of alkyl chlorobiphenylyl ethers some of which are alkyl polychlorobiphenylyl ethers. These ethers can be depicted as having an average general formula of the type Cl: (OR),-

wherein R is a lower alkyl radical having from 1 to 4 carbon atoms; y is an average number of from about 0.1 to about 2.0; x is an average number of from about 1.0 to 4.0 and wherein the sum of x plus y equals the average number of a chlorine substituent in the chlorinated biphenyl starting material.

The chlorinated biphenyls generally useful as starting materials for this invention may be prepared by the direct chlorination of biphenyl in the presence of an appropriate catalyst, e.g., an iron catalyst, to produce compositions containing from about 35 percent to about 55 percent, preferably containing from about 40 percent to about 55 percent of chlorine, as for example as described in US. Patent No. 1,892,397. A typical chlorinated biphenyl containing about 42 percent of combined chlorine was found by vapor phase chromatographic analysis to consist of the following components expressed in mole percent: 2,2 dichlorobiphenyl 3.3%; 2,4 dichlorobiphenyl 0.2%; 2,5-dichlorobiphenyl 0.2%; 2,3-dichlorobiphenyl 0.1%; 2,4-dichlorobiphenyl 8.7%; 3,4-dichlorobiphenyl 0.1%; 4,4-dichlorobiphenyl 6.0%; 2,6,2'-triclilorobiphenyl 1.7%; 2,4,2-trichlorobiphenyl 4.0%; 2,5,2 trichlorobiphenyl 3.2%; 2,4,4 trichlorobiphenyl 12.4%; 2,5,4-trichlorobiphenyl 6.0%; 3,4,2'-trichlorobiphenyl 4.8%; 2,3,4-trichlorobiphenyl 2.4%; 2,4,4-trichlorobiphenyl 8.1%; other 2,4 X trichlorobiphenyl 2.3% and tetrachloro-biphenyls 24.6%. The term 2,4-X- trichlorobiphenyl employed in the instant specification means that the compound is a biphenyl molecule having a chlorine atom substituent at the 2 and 4 positions and additionally a third chlorine atom at one of the remaining available positions which third position is designated by X. g

Alkali metal alkoxides useful in the reaction may be lithium, potassium, sodium, rubidium or cesium alkoxides, with potassium and sodium allzoxides being preferred. The allcoxides may be those of a primary, secondary, or tertiary alcohol with those of primary alkanols being preferred.

An important aspect of this invention and one which has been found to be essential to the success of the reaction as shown by the examples given below, is to conduct the reaction in the presence of a diluent or solvent which is a dialkyl ether of an alkylene glyool having from 1 to 4 alkylene groups, from 2 to 4 carbon atoms in each alkylene group, and from 1 to 4 carbon atoms in each alkyl group. The term alkylene glycol is used herein in its generic sense to include the mono-, di-, tri-, and tetraalkylene glycols, the dialkyl ethers of which have been found to be useful to eifect the etherification reaction of the invention. Examples of useful diluents or solvents include the dimethyl, diethyl, dipropyl, diisopropyl, dibutyl and diisobutyl ethers of ethylene glycol, propylene glycol, butylene glycol, isobutylene glycol, diethylene glycol, dipropylene glycol, diischutylene glycol, triethylene glycol, tripnopylene glycol, tributylene glycol, tetraethylene glycol, tetrapropylene glycol, tetrabutylene glycol, etc. Other useful ether solvents which are dialkyl ethers of alkylene glycols are the mixed alkyl ethers, e.g., bis(2-ethoxypropyl)ether, and bis[2-(2-methoxyethoxy) ethyl]ether, etc. Why the use of such a solvent is necessary for the accomplishment of this reaction is not understood. However, applicants have found that when no solvent is used, or a hydroxylic solvent is employed, no displacement reaction occurs.

Reaction of the chlorinated biphenyl composition with an alkali metal alkoxide of the types described above to give the present alkyl chlorobiphenylyl ether compositions takes place, according to this invention, by employing as diluent or solvent a dialkyl ether of an alkylene glycol of the type described above, and heating the reaction mixture at a temperature of from, say, about 130 C. to about 250 C., at ordinary, decreased or increased pressure until formation of the alkyl chlorobiphenylyl ether has taken place, temperature in the lower part of the given range being generally useful with the lower pressures and the higher temperatures with the higher pressure. However, ordinarily, the reaction proceeds satisfactorily at atmospheric pressure by refluxing the reaction mixture for a time sutficient to effect the etherification reaction to the desired extent. Since the reaction may result in the replacement of more than one chlorine atom by the alkoxy radical, when desiring a preponderance of the substitution of an average of less than one chlorine atom by any alkoxyl group, it is generally advisable to use a large excess of the chlorinated biphenyl starting material. On the other hand, when the major product desired is an alkyl chlorinated biphenylyl ether composition having an average alkoxy content of greater than 1.0, the alkali metal alkoxide is advantageously used in greater than an equimolar proportion. The lay-product is an easily separatable alkali metal chloride.

The reaction time and temperature appears to have little, if any, effect upon the nature of the ether product. Although a primarily formed monoether will react with another mole of the alkali metal alkoxide to yield a diother, higher temperatures of continued heating alone do not suffice in elfecting substantial conversion to the diether. An excess of the alkali metal alkoxide over that required for the replacement of one chlorine atom should be present in order to obtain any substantial formation of the diether. Whether the reactant quantities present are those which favor mono-substitution (excess of chlorinated biphenyl) or whether the proportions are such as to favor di-substitution (excess of the alkali metal alkoxide), ether formation occurs after heating at a temperature of from about 130 C. to about 250 C. and preferably of from 160 C. to 210 C. for a time of say, several hours to a day. The progress of the reaction can be generally followed by noting the cessation of change in the refractive index of the reaction mixture. Although, as stated above, reaction of the chlorinated biphenyl composition and the alkali metal alkoxide can be so directed as to result in a preponderance of product having an average of less than one or more than one ether group based on the average number of chloro groups present in the product, generally the product contains a mixture of monoand di-ethers in varying proportions.

The present alkyl chlorobiphenylyl ether compositions are stable, rather high-boiling liquids which are useful for a variety of industrial purposes, but which are particularly valuable as liquid dielectric compositions. They are advantageously employed as liquid impregnants in capacitor and cable manufacture, as transformer coolants and in the fabrication of switch gear. Characteristics of the present compositions are such as to render them particularly valuable as impregnants for cellulosic insulating material. It is known in the art that the impregnation of cellulosic materials, for example Wood pulp, paper, cotton, cotton fabric, cellulose acetate fibers and textiles, by certain liquid dielectrics provides an insulating material which has a dielectric strength which is much higher than that of either the cellulosic material before impregnation or the liquid dielectric. Some of the first liquids used for this purpose were mineral oils, the dielectric strength of oil-impregnated paper having been reported by Bailey (Radio Engineering, volume 17, page 35 (1937)) to be 15 times as high as that of the oil alone. However, because mineral oils are readily oxidized, their usefulness as insulating media and as impregnating agents for cellulosic materials has been limited in that exposure to air, sunlight and moisture often leads to gas formation, gaseous ionization and formation of wax. These changes affect power factor stability.

Although wood pulp paper, alone, has good insulating properties, it is also affected by exposure to air, particularly at higher temperature. When the rate of mechanical deterioration is reduced by impregnating the insulation with oil, this was of little advantage as noted above. Accordingly, the art resorted to other impregnating agents, particularly the highly chlorinated aromatic hydrocarbons. In addition these materials are non-flammable and more stable to the influence of air, moisture and light. The present invention provides a method of increasing the dielectric constant values of the chlorinated biphenyls.

The presently provided mixtures of chlorinated biphenyl and alkyl chlorobiphenylyl ethers are high boiling materials which possess high resistivities and low power factors. Their stability to high temperatures is evidenced by little or no change in power factor readings after heating for 24 hours at C. Their stability is further illustrated by continued high resistivities which indicates freedom from conducting ions which would be present if decomposition of the mixtures occurred. The presently provided compositions remain liquid at low temperatures, whereby there is avoided a decrease in dielectric constants due to freezing of the dipolar motion.

The above characteristics thus speak for eminent suitability of the compositions of this invention as impregnating agents for cellulosic materials and an embodiment of the present invention is the provision of improved cellulosic insulating agents comprising porous materials derived from cellulose, for example, pulps, fibers, textiles, or papers derived from Wood, cotton, or linen, which porous products have been impregnated with the present mixtures of chlorinated biphenyl and alkyl chlorobiphenlyl ethers.

Examples of electrical apparatus in which the present alkyl chlorobiphenylyl ether compositions are valuable components are shown in the accompanying drawing.

FIGURE 1 is a front elevation partly in section of a transformer; FIGURE 2 illustrates a switch in a similar manner; FIGURE 3 represents a rolled capacitor; FEGURE 4 shows a sectional view of a portion of the electrode and dielectric sheets of FIGURE 3; and FIGURE 5 is a side view of a cable, the casing being partly removed to permit the interior of the parts to be seen.

The transformer illustrated in FIGURE 1 comprises a casing 1, core 2, coils 3 insulated with manila paper, kraft paper, cotton or other fibrous insulation, insulating and cooling medium 4, lead in bushings 5, and suitable leads 6 connected to the coil assembly. The insulating and cooling medium in the transformer of this invention is a mixture of the chlorinated biphenyl and alkyl chlorobiphenylyl ether of the type described above. Liquid hydrocarbons or other halogenated hydrocarbons or mixtures thereof may also be used in combination with the compositions described hereinabove as dielectric media,

for example, petroleum oil, halogenated compounds of naphthalene, toluene, benzene, nitrobiphenyl or diphenyl ether.

The switch shown in FIGURE 2 comprises a casing 7, fixed contacts 8 and 9, and movable contacts '10 and 11, which cooperate therewith. The movable contacts are mounted upon the support 12 which in turn is operatively connected to actuating levers 13. Suitable arcquenching liquids which may be used in this device, either as the sole dielectric, or in combination with a minor proportion of petroleum oil or a chlorinated hydrocarbon are, e.g., a mixture of chlorinated biphenyl and methyl chlorobiphenylyl ether or isopropyl chlorobiphenylyl other as described hereinabove.

The capacitor shown in FIGURE 3 is made up of alternate layers of metal foil such as aluminum or tinfoil, separated by sheets of dielectric material. FTGURE 4 shows a section of one turn of the finished roll capacitor illustrating the alternate electrode and dielectric layers. Details of the construction of the paper capacitor are set forth by way of illustration;

Three sheets of tissue paper (preferably kraft capacitor tissue) are stacked upon each other, and a thin aluminum foil (about 0.003 inch in thickness) is laid upon the top sheet of tissue. The foil is than covered with three more sheets of the tissue and another sheet of the foil is placed thereon so that the two sheets of metal foil are separated from each other by the tissues. On the second metal sheet there are stacked three more sheets of said tissue and a stack of alternating layers of metal foil and tissue thus obtained is wound into a cylindrical roll. This is placed in a container, and at this point electrical connecting means, for example wire and bar conductors, depending upon the size of the assembly, may be connected through the metal foil in known manner. After drying, preferably in a heated vacuum oven, one or more of the present alkyl chlorinated biphenyl ether compositions is added to the container in a quantity suificient to impregnate thoroughly the paper content thereof. The container is then sealed.

Alternatively, and particularly in the manufacture of small resistors which for the sake of economy are housed in paper tubes rather than in leak-proof containers, the tissue paper is impregnated with the alkyl chlorinated biphenyl ether composition previous to interleafing with the metal foil in the manner described above.

The invention is further illustrated but not limited by the following examples.

Example 1 To a mixture of 40.5 grams (0.75 mole) of sodium methoxide and 500 ml. of diglyme (the dimethyl ether of diethylene glycol) as solvent, was added 128.5 g (0.5 mole) of a chlorinated biphenyl having 42% by weight of combined chlorine. The mixture was heated at reflux (162 C.) for 22 hours. After cooling, the mixture was filtered and the solids were washed with ether. The filtrates were combined and the ether and diglyme were removed by distillation. The residue was distilled yielding 81.8 grams of a mixture of the starting chlorinated biphenyl and methyl chlorobiphenylyl ether, B.P. 130 C. to 155 C./0.5 mm 1113 1.6075, having a dielectric constant of 7.45 at 100 kc. and 25 C. and a pour point of C. Analysis showed said mixture contained an average of 0.94 methoxy units per biphenyl unit, or a 64.7% yield of ether based on the alkoxide.

Example 2 A mixture of 73 g. (0.25 mole) of chlorinated biphenyl having 48% of combined chlorine, 27 g. (0.5 mole) of sodium methoxide and 250 ml. of diglyme was heated at reflux for 18 hours. After cooling, the mixture was filtered and the solids washed with ether. The filtrates were combined and the ether and the diglyme were evaporated. The residue was distilled to yield 48 grams (68% theoretical yield) of a mixture of the starting chlorinated biphenyl and methyl chlorobiphenylyl ether, B.P. point 142-187 C./0.6 mm. having a dielectric constant of 7.92 at kc. and 25 C. and a pour point of -1 C. Analysis showed 1.6 methoxy units per biphenyl unit in the mixture.

Example 3 A mixture of 81.6 grams (0.25 mole) of a chlorinated biphenyl having 54% of combined chlorine and 27 grams (0.5 mole) of sodium methoxide in 250 ml. of diglyme was heated at reflux for 21 hours. After cooling, the mixture was filtered and the solids washed with ether. The filtrates were combined and the ether and diglyme evaporated. The residue was distilled yielding 41.6 grams of a mixture of the starting chlorinated biphenyl and the methyl chlorobiphenylyl ether, B.P. to 185 C./0.6 mm, having a dielectric constant of 6.7 at 100 kc. and 25 C. The introduction of 1.47 methoxy units per biphenyl unit was determined by chlorine analysis. This represents a 52.5% yield of ether product based on the alkoxide.

Example 4 Sodium (10 grams, 0.44 mole) was added to 200 ml. of isopropyl alcohol and the mixture heated until reaction was completed. The sodium isopropoxide solution thus obtained was then added to a solution of 10 3 grams (0.4 mole) of a 42% chlorinated biphenyl in 350 ml. of diglyme. The excess isopropyl alcohol was removed by distillation and the diglyme solution was heated at reflux C.) for ten hours. After cooling, the mixture was filtered, the filtrate evaporated to a small volume and the residue partitioned between methylene chloride and water. The methylene chloride was washed with water, dried over magnesium sulfate and evaporated to a small volume. The residue was distilled yielding 78.8 grams of a mixture of starting chlorinated biphenyl and isopropyl chlorobiphenyl ether, B.P. 118145 C./0.3 mm., having a dielectric constant of 6.6 at 100' kc. and 25 C. and a pour point of -18 C. The introduction of 0.54 alkoxy units per biphenyl unit was determined. A 70.4% yield of ether product was thus obtained.

Example 5 This example illustrates the eifect of attempting to carry out the reaction between a chlorinated biphenyl with an alkali metal alkoxide in the absence of a solvent.

To 128.5 grams of a chlorinated biphenyl containing approximately 42% combined chlorine there was added 40.5 grams of sodium methoxide and the resulting mixture was warmed and stirred at 165 C. for 22 hours. After cooling, water was added and the aqueous organic layers were filtered and separated. The organic layer was washed again with water and then distilled to obtain 120.4 grams (95% recovery) of liquid, analyzing 42.62% chlorine which indicated that no reaction took place.

Example 6 This example illustrates the effect of attempting to carry out the reaction between the chlorinated biphenyl and an alkali metal alkoxide in the presence of methanol as a solvent.

A mixture of 51.4 grams of a chlorinated biphenyl containing approximately 42% of combined chlorine and 10.8 grams of sodium methoxide in 25 ml. of methanol was heated at reflux (approximately 100 C.) for 18 hours. Chlorine analysis of the washed distilled product showed that no reaction had occurred.

Example 7 This example illustrates an attempt to carry out the re action between the chlorinated biphenyl and an alkali metal alkoxide in the presence of ethylene glycol as a solvent.

scenes? To a mixture of 77.1 grams of a chlorinated biphenyl containing 42% combined chlorine in 250 ml. of ethylene glycol there was added 27.0 grams of sodium methoxide. The mixture was heated at reflux for 19.5 hours. The chlorinated biphenyl starting material and ethylene glycol were immiscible even at temperatures of up 140 C. and hence even after long heating no reaction was evide-nced.

Example 8 This example illustrates how a chlorinated biphenyl having a relatively high dielectric constant may be treated according to this invention to obtain a product having a still higher dielectric constant. A mixture of chlorinated biphenyls having a dielectric constant of 7.20 at 100 kc. and 25 C. was prepared by chlorinating 2,4-dichloro biphenyl as described in the cope-riding application of Harold I. Weingarten, Serial No. 818,530, filed June 8, 1959, now Patent No. 3,038,107. To 42.7 grams of this mixture there was added 175 ml. of diglyrne solvent, 3.9 grams of sodium metal and 60 ml. of methanol. The excess methanol was distilled off as the temperature rose to approximately 170 C. The reaction mixture was refluxed at this temperature for 4 hours and then allowed to cool overnight. The diglyme solvent was then evaporated and the residue was partitioned between methylene chloride and water. The methylene chloride solution was washed with water, dried over magnesium sulfate and evaporated to dryness. The crude product was distilled to obtain 30.7 grams of a mixture of chlorinated biphenyl and methyl chlorobiphenylyl ether, BP. 120 to 145 C./ 0.7 mm., and having a dielectric constant of 7.6 at 25 C. and 100 kc.

Products obtained by the reaction of chlorinated biphenyl materials with alkali metal alkoxides using a dialkyl ether of an alkylene glycol as a diluent had consistently higher dielectric constants (Dk) than the starting chlorinated biphenyls. Further, when no solvent was used in the reaction mixture no methoxy group replacement of chlorine in the starting material took place. Similarly, when solvents other than those of the described type were used, for example when methanol, ethylene, glycol, etc. were used, no etherification was obtained. Examples of methyl chlorinated biphenylyl ether product compositions obtained according to the method of this invention are illustrated as follows by the following table:

1 Chlorinated biphenyl having from 40 to 42 percent combined chlorine.

Although the present ethers are particularly useful as impregnating agents for cellulosic materials adapted for use as dielectrics, because of their very good electrical properties, their thermal stability and their ability to remain liquid at low temperatures, they are of general utility as liquid dielectrics. They are likewise very advantageously employed as functional fluids, for example, as heat transfer media and as hydraulic fluids.

We claim:

1. A composition of matter consisting essentially of a mixture of chlorinated biphenyls and an alkyl chlorobiphenylyl ether having from 1 to 4 carbon atoms in the alkyl radical, said composition having been prepared by reacting a chlorinated biphenyl composition containing from about 35 to about 55% by weight of combined chlorine with an alkali metal alkoxide having from 1 to 4 carbon atoms in the alkoxide group, in the presence of a solvent which is a dialkyl ether of an alkylene glycol having from 1 to 4 alkylene groups and from 2 to 4 carbon atoms in each alkylene group at a temperature of from about C. to 250 C. until an average of from about 0.1 to 2.0 alkyl ether groups per molecule have been introduced, and then removing the solvent.

2. A composition of matter consisting essentially of a mixture of chlorinated biphenyls and a methyl chlorobiphenylyl ether, said composition having been prepared by reacting a chlorinated biphenyl composition containing from about 35% to about 55% by weight of combined chlorine with sodium methoxide, in the presence of a solvent which is the dimethyl ether of diethylene glycol at a temperature of from about 130 C. to about 250 C. until an average of from about 0.1 to about 2.0 methyl ether groups per molecule have been introduced, and removing the solvent.

3. A composition of matter consisting essentially of a mixture of chlorinated biphenyls and an isopropyl chlorobiphenylyl ether, said composition having been prepared by reacting a chlorinated biphenyl composition containing from about 35 to about 55% by weight of combined chlorine with sodium isopropoxide in the presence of a solvent which is the dimethyl ether of diethylene glycol at a temperature of from about 130 C. to about 250 C. until an average of from about 0.1 to about 2.0 isopropyl ether groups per molecule have been introduced, and removing the solvent.

4. A process for preparing improved dielectric compositions which comprises reacting a chlorinated biphenyl composition having from about 35 to about 55% of combined chlorine with an alkali metal alkoxide having from 1 to 4 car-hon atoms in the alkoxide radical, in the presence of a solvent which is a dialkyl ether of an alkylene glycol having from 1 to 4 alkylene groups and from 2 to 4 carbon atoms in each alkylene group at a temperature of from about 130 C. to 250 C. until an average of from about 0.1 to 20- alkyl ether groups per molecule have been introduced, and then removing the solvent.

5. A method according to claim 4 wherein the reaction is effected at a temperature ranging from about 130 C. to about 250 C.

6. A method for preparing an improved dielectric composition which comprises reacting a chlorinated biphenyl composition having from about 35% to about 55 by weight of combined chlorine with sodium methoxide, employing as diluent a dimethyl ether of diethylene glycol at a temperature of from about 130 C. to about 25 0 C. until an average of from about 0.1 to about 2.0 methyl ether groups per molecule have been introduced, and removing the diluent.

7. A method according to claim 4 wherein the reaction is eliected at a temperature of from about C. to C.

8. A method for preparing an improved dielectric com position which comprises reacting a chlorinated biphenyl composition having from about 35% to about 55% by weight of combined chlorine with sodium isopropoxide employing as diluent a dimethyl ether of diethylene glycol at a temperature of from about 130 C. to about 250 C. until an average of from about 0.1 to about 2.0 isopropyl ether groups per molecule have been introduced, and removing the diluent.

9. A dielectric comprising a cellulosic material impregnated with a composition of matter described in claim 1.

10. Electrical apparatus comprising, in combination, metallic conducting elements disposed in spaced relationship to each other and adapted during operation of the apparatus to have a difference in electrical potential therebetween and, interposed between said elements for insulating one from the other, a liquid dielectric medium 9 Consisting essentially of a composition of matter described in claim 1.

11. A capacitor consisting essentially of a pair of electrodes and an insulating agent associated with each of the electrodes and isolating them from each other, said insulating agent comprising the dielectric composition defined in claim 9.

12. A capacitor comprising a pair of electrodes and an insulating agent associated with each of the electrodes and isolating them from each other, said insulating agent consisting essentially of a cellulosic material impregnated with a composition of matter defined in claim 2.

13. A capacitor comprising a pair of electrodes and an insulating agent associated with each of the electrodes and isolating them from each other, said insulating agent consisting essentially of a cellulosic material impregnated with a composition of matter defined in claim 3.

14. A method for improving the dielectric constant of a chlorinated biphenyl composition containing from about 35% to about 55% by weight of combined chlorine which comprises treating said chlorinated biphenyl composition with an alkali metal alkoxide having from 1 to 4 carbon atoms in the alkoxide group in the presence of a solvent which is a dialkyl ether of an alkylene glycol having from 1 to 4 alkylene groups and from 2 to 4 carbon atoms in each alkylene group until an average of about 0.1 to 2.0 alkyl ether groups per molecule have been introduced, and removing the solvent.

References Cited in the file of this patent UNITED STATES PATENTS 1,887,757 Gretner Nov. 15, 1932 2,028,081 Stoesser Jan. 14, 1936 2,130,527 Coleman et al Sept. 20, 1938 2,193,614 Alexander Mar. 12, 1940 2,248,491 Coleman et al. July 8, 1941 

1. A COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF A MIXTURE OF CHLORINATED BIPHENYLS AND AN ALKYL CHLOROBIPHENYL ETHER HAVING FROM 1 TO 4 CARBON ATOMS IN THE ALKYL RADICAL, SAID COMPOSITION HAVING BEEN PREPARED BY REACTING A CHLORINATED BIPHENYL COMPOSITION CONTAINING FROM ABOUT 35% TO ABOUT 55% BY WEIGHT OF COMBINED CHLORINE WITH AN ALKALI METAL ALKOXIDE HAVING FROM 1 TO 4 CARBON ATOMS IS THE ALKOXIDE GROUP, IN THE PRESENCE OF A SOLVENT WHICH IS A DIALKYL ETHER OF AN ALKYLENE GLYCOL HAVING FROM 1 TO 4 ALKYLENE GROUPS AND FROM 2 TO 4 CARBON ATOMS IN EACH ALKYLENE GROUP AT A TEMPERATURE OF FROM ABOUT 130*C. TO 250*C. UNTIL AN AVERAGE OF FROM ABOUT 0.1 TO 2.0 ALKYL ETHER GROUPS PER MOLECULAR HAVE BEEN INTRODUCED, AND THEN REMOVING THE SOLVENT. 